In the manufacture of miniature electrical fuses having a generally centered fuse element within a cylindrical housing bore as distinguished from diagonally extending fuse elements, it is desirable that the element be reasonably well centered within the bore so that the fuses of a given type will have uniform blowing characteristics. A variety of well-known methods are used for centering fuse elements. In larger fuse structures, such methods include the use of perforated disks or plugs at either end of the housing bore provision of such plugs or disks adds to the cost of manufacture, and becomes increasingly difficult to implement as applied to fuses of extremely small dimension, such as cylindrical fuses having a housing length (body length) in the range of 5 mm. or so and having a corresponding bore diameter of the order of 1 mm.
An additional problem arises from the use of solder to attach the ends of the fuse element to the fuse terminal end caps. A preferred method of manufacture of, for example, cartridge-type cylindrical fuses is to provide a quantity of molten solder within a terminal forming end cap, to slide the cylindrical fuse housing into it, thereafter followed by the fuse element itself, after which the solder is fused to capture the end of the fuse in the cap. In the event that the end of housing itself is coated by a material which is wet by the solder, the solder will also adheringly capture the housing. A similar procedure is applied to secure the retaining ends of the housing and the fuse element to a second end cap. In the event that a housing material is employed which is not wet by the solder, the final structure may be encapsulated by an encapsulating resin by well-known methods, such as for example as set forth U.S. Pat. No. 4,385,281, issued May 24, 1983, to McAlear, et. al., the teachings of which are incorporated by reference herein.
The problem with such fabrication methods, although they are readily suited to mass-production, lies in the fact that a sufficient pool of solder must be provided in each cap to captively secure the fuse element ends, with the result that when the solder is melted and the housing and fuse element end are forced to a seated position within the end cap, it is frequently observed that a quantity of solder is splashed along the outer surface of the fuse housing body beyond the confines of the cap, requiring a subsequent solder removal operation. This undesirable exuding of solder is particularly noted when the second fuse cap is soldered to the structure, since the housing interior is now sealed, and gas venting augments this process. This problem is particularly objectionable in miniature fuses of dimensions as set forth above, since solder removal operations are extremely difficult with such small structures.
In addition to the problem of excess solder removal, a far more serious problem arises in conventional fuse designs because of the aforementioned gas venting, since in such designs such gas venting is observed on occasion to be sufficient to carry the entire volume of solder surrounding the fuse element completely away from it. A significant mass of solder should always remain emplaced around the fuse element to safely secure it to the interior surfaces of the fuse cap. A loss of this body frequently results in a fragile fuse structure.
The instant invention is oriented towards an inexpensive, reliable means of solving both of the aforementioned problems.